1. Field of the Invention
The present invention relates to an optical head which can be used for an optical disk apparatus performing reproduction and/or recording of data through use of a laser beam, and performs reading and/or recording of a signal, and also to a method for producing the same.
2. Description of the Related Art
Recently, optical disk media have been practically used as high-capacity data files. Realization of optical disk media having a higher capacity has been desired in order to widen the range of applications thereof. Regarding a recording density of an optical disk apparatus, the partial response technology has put to practical use a recording density of about 0.3 .mu.m/bit for a linear density direction and a recording density of about 1.2 .mu.m/track for a track direction.
An improvement in the recording density of the optical disk apparatus can be realized by a reduction in the size of a light spot formed on an optical disk medium by a light beam which is converged by an optical head. Such a size of the light spot formed by the optical head is generally determined by a wavelength of a light source and an aperture of a converging lens. Accordingly, various systems in which the size of the light spot is reduced through an improvement in these parameters in order to improve the recording density of the optical disk apparatus have been proposed.
In one of these proposed systems, such as that disclosed in Japanese Laid-Open Publication No. 5-135401 and U.S. Pat. No. 5,590,110, light reflected from the optical disk medium is converged again using a lens, and only the light in a central portion of the converged light beam is separated and detected by being passed through a pinhole region of a pinhole filter. Such a system enables a signal to be reproduced with a resolution higher than an original resolution determined by the wavelength of the light source and the aperture of the converging lens employed in the optical system, thereby making possible the realization of a high-density optical disk apparatus.
In the following, this system is referred to simply as "optical head super-resolution reproducing system."
In the optical head super-resolution reproducing system according to the conventional technology, it is necessary that the pinhole region of the pinhole filter be aligned with the central portion of the converged light beam with high precision on the order of a micron. In this case, the alignment in the focal length direction from the lens can be realized easily to some extent by arranging the pinhole filter at a design-based, prescribed position. However, in order to obtain sufficient functioning of the optical head super-resolution reproducing system, it is necessary that the converged light beam precisely pass through the minute pinhole region of the pinhole filter. This requires that the pinhole filter be precisely two-dimensionally aligned in a plane which is spaced from the lens by a focal length and is perpendicular to an optical axis (this plane may be referred to as "focal length plane" in the following).
In reality, however, it is impossible to achieve a sufficient level of precision in such alignment of the pinhole region (especially, the two-dimensional alignment in the focal length plane). Consequently, it is extremely difficult to put the optical head super-resolution reproducing system into practical use.